When rolled out in a reversing rolling mill, strips coiled on reels are normally rolled with high strip tensions. The strip tensions are applied by the reels, alternately acting as coilers and uncoilers. To enable the tensions to be introduced into the strip on the coils, at least approximately 1.5 to 2 windings of the strip are coiled on the coiling reel prior to the start of rolling or left on the uncoiling reel at the end of each reduction pass. Those lengths of the strip to be rolled which are situated on the reel and also the strip length between the reels and the rolling mill remain unrolled. Since they are of the wrong dimensions, unrolled strip lengths with the thickness of the starting material are cut off on completion of rolling and represent an appreciable loss of material.
To obviate or at least clearly reduce the cutting-off of the strip ends of incorrect dimensions and the resulting loss of material, various methods have been developed for the rolling-out of the strip ends. In such methods known to the Applicants from practice the start and end of the strip are rolled out without strip tension.
In a first method the start of the strip is rammed to the preadjusted roll gap. Ramming is performed, for example, by means of driving rolls of different kinds or by means of ramming carriages. The rolled start of the strip is guided via deflecting flaps into a clamping slot of the coiling reel, when it is clamped and automatically coiled on. When 1 to 2 strip windings have been coiled, the required strip tension is applied on the inlet and outlet sides and the rolling operation continued with the required strip tension. Correspondingly, at the end of each reduction pass, when 1 to 2 residual windings have been completed on the unwinding reel, the inlet side strip tension is reduced to 0, the strip clamping on the uncoiling reel is released and the strip end is rolled until it leaves the roll gap. In the following reduction pass, this strip end forming the start of the strip is rammed into the roll gap as described. Such a method is known from JP-A 60-244417.
One disadvantage of that method is that malfunctions may occur when the start of the strip is rammed into the roll gap. For example, during insertion the start of the strip may become kinked and is therefore not rolled. Furthermore, when it leaves the roll gap, the rolled strip may be bent upwards or downwards like the tip of a ski and then be driven into the roll stand guides. Yet another disadvantage is that in the case of thin strips and high rolling forces, the prestressed rolls may collide and become damaged when the strip end runs out of the roll gap. To obviate the disadvantages described, in another method the strip ends are not rolled out over their whole length, but are halted immediately before they reach the roll gap. An unrolled piece of strip with the thickness of the starting material is therefore left, but it is short in comparison with the strip ends in the first-mentioned prior art method.
One disadvantage of this method is that the unrolled strip end, which is bent by the clamping slot of the uncoiling reel, remains bent, so that fresh insertion in the clamping slot is not readily possible. Nevertheless, to enable the strip end to be introduced into the clamping slot again, truing rolls are used which correct the kink caused by the clamping to such an extent that the start of the strip can be reinserted in the clamping slot. However, in the case of a very strong material the clamping slot cannot be aligned in this way.
In another prior art method wherein the strip end is also halted shortly before it reaches the roll gap, the strip end containing the kink from the clamping slot is cut off, for example, by means of cropping shears.
A disadvantage of the last-mentioned method is the considerable length lost, which comprises the unrolled piece of strip at each strip end, which corresponds to the distance between the cropping shears and the roll gap, and the ends cut off after each reduction pass. Another disadvantage is that the pieces of strip cut off must be disposed of for every reduction pass.
It is an object of the invention to provide a method and an apparatus for rolling out the ends of a coiled strip in a reversing rolling mill, whereby the lengths lost at the strip ends are small. Another object is to enable the method to be performed using the most inexpensive apparatus possible.